Add pickle metadata to blob literal

[pingsutw]

TL;DR

propeller can use this metadata to know how many pods to launch in the map task.

Type

• Bug Fix
• Feature
• Plugin

Are all requirements met?

• Code completed
• Smoke tested
• Unit tests added
• Code documentation added
• Any pending items have an associated Issue

Complete description

How did you fix the bug, make the feature etc. Link to any design docs etc

Tracking Issue

NA

Follow-up issue

NA

[codecov]

Codecov Report

Merging #409 (b992d95) into master (9d79003) will increase coverage by 2.57%.
The diff coverage is 100.00%.

❗ Current head b992d95 differs from pull request most recent head 60cc28d. Consider uploading reports for the commit 60cc28d to get more accurate results

@@            Coverage Diff             @@
##           master     #409      +/-   ##
==========================================
+ Coverage   75.90%   78.48%   +2.57%     
==========================================
  Files          18       18              
  Lines        1457     1250     -207     
==========================================
- Hits         1106      981     -125     
+ Misses        294      212      -82     
  Partials       57       57              

Flag	Coverage Δ
unittests	?

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Impacted Files	Coverage Δ
clients/go/admin/config_flags.go	61.22% <100.00%> (+3.22%)	⬆️

... and 17 files with indirect coverage changes